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206-00-29
Brake System
-
General Information
206-00-29
DIAGNOSIS AND TESTING
and repair the external leak. If the fluid level drops
and no external leak can be found, check for a
brake master cylinder bore end seal leak.
Brake System Check
Brake Pedal Reserve Check
Where a low brake pedal or the feel of a
bottomed-out condition exists, check for brake
pedal reserve.
1. Operate the engine at idle with the transaxle in
NEUTRAL.
2. Apply the brake pedal lightly three or four times.
3. Allow 15 seconds for vacuum to replenish the
brake booster.
N0TE:This increased resistance may feel like
something has bottomed out.
4. Apply the brake pedal until it stops moving
downward or an increased resistance to the
pedal travel occurs.
5. Hold the brake pedal in the applied position and
raise the engine speed to approximately 2000
rpm.
N0TE:The additional movement of the brake pedal
is the result of the increased engine intake manifold
vacuum which exerts more force on the brake
booster during engine rundown. This means that
additional stroke is available in the brake master
cylinder and the brake system is not bottoming out.
6. Release the accelerator pedal and observe that
the brake pedal moves downward as the engine
returns to idle speed.
Brake Booster Functional Test
lnspect all hoses and connections. All unused
vacuum connectors should be capped. Hoses and
their connections should be correctly secured and
in good condition with no holes and no collapsed
2. With the transaxle in NEUTRAL, stop the engine
and apply the parking brake. Apply the brake
pedal several times to exhaust all vacuum in
the system.
3. With the engine turned off and all vacuum in the
system exhausted, apply the brake pedal and
hold it down. Start the engine. If the vacuum
system is operating, the brake pedal will tend
to move downward under constant foot
pressure. If no motion is felt, the vacuum
booster system is not functioning.
4. Remove the vacuum hose from the brake
booster. Intake manifold vacuum should be
available at the brake booster end of the hose
with the engine at idle speed and the transaxle
in NEUTRAL. Make sure that all unused vacuum
outlets are correctly capped, hose connectors
are correctly secured and vacuum hoses are in
good condition. When it is established that
manifold vacuum is available to the brake
booster, connector the vacuum hose to the
brake booster and repeat Step 3. If no
downward movement of the brake pedal is felt,
install a new brake booster. REFER to: (206-07
Power Brake Actuation)
Brake Booster
-
LHD (Removal and lnstallation),
Brake Booster
-
RHD (Removal and lnstallation).
5. Operate the engine a minimum of 10 seconds
at fast idle. Stop the engine and let the vehicle
stand for 10 minutes. Then, apply the brake
pedal with approximately 89 N (20 lb) force. The
pedal feel (brake application) should be the
same as that noted with the engine operating.
If the brake pedal feels hard (no power assist),
install a new vacuum check valve and then
repeat the test. If the brake pedal still feels hard,
install a new brake booster. REFER to: (206-07
Power Brake Actuation)
Brake Booster
-
LHD (Removal and Installation),
Brake Booster
-
RHD
e em oval
and installation).
If the brake pedal movement feels spongy, bleed
the brake system. REFER to: (206-00 Brake
System
-
General Information)
areas. Inspect the check valve on the brake booster
Brake System Bleeding (General Procedures),
for damage.
Brake System Pressure Bleeding (General
Procedures).
Brake Booster Operation Check
Brake Master Cylinder
1. Check the hydraulic brake system for leaks or
low fluid.
Usually, the first and strongest indicator of anything
wrong with the braking system is a feeling through
the brake pedal. In diagnosing the condition of the
brake master cylinder, check pedal feel as
2006.0 Fiesta
1212006
G28494en
I
i
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